package java行为型设计模式.观察者模式;

import java.util.ArrayList;
import java.util.List;

/**
 *
 观察者模式用于在一个对象被修改时通知其相关对象。

 观察者模式是一种行为模式类别
 */
public class Main {
    public static void main(String[] args) {
        MyValue subject = new MyValue();
        new FileObserver(subject);
        new EmailObserver(subject);
        new PrinterObserver(subject);

        subject.setState(15);

        subject.setState(10);
    }
}
class MyValue{
    private List<Observer> observers = new ArrayList<>();
    private int state;
    public int getState(){
        return state;
    }
    public void setState(int state){
        this.state  = state;
        notifyAllObservers();
    }
    public void attach(Observer observer){
        observers.add(observer);
    }
    public void notifyAllObservers(){
        for (Observer observer : observers) {
            observer.update();
        }
    }

}
abstract class Observer{
    protected MyValue subject;
    public abstract void update();
}
class PrinterObserver extends Observer {
    public PrinterObserver(MyValue subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Printer: " + subject.getState());
    }
}
class EmailObserver extends Observer {

    public EmailObserver(MyValue subject){
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Email: "+ subject.getState() );
    }
}
class FileObserver extends Observer {

    public FileObserver(MyValue subject){
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("File: " + subject.getState());
    }
}
